Photoreduction and -Oxidation of Molecular Nitrogen on Titanium Dioxide and Titanium Containing Minerals

Photon-Driven Nitrogen Fixation: Current Progress, Thermodynamic Considerations, and Future Outlook

“…Interestingly, the stoichiometric results of Figure indicate that nitrogen reduction effectively competes with hydrogen evolution. The H 2 :NH 3 selectivity here was speculated to depend on pretreatment temperature which affected the rutile/anatase ratio . Selectivity toward ammonia over hydrogen has been identified as a key challenge in electrochemical ammonia synthesis, , suggesting that rutile TiO 2 exhibits a low overpotential for nitrogen reduction and a high overpotential for hydrogen evolution.…”

“…The ammonia yield of pure rutile was found to be about twice that of anatase. , This decrease was attributed to a loss of rutile surface area because photocatalysts with a larger percentage of rutile generally consist of larger titania particles. The optimal rutile particle size was determined to be 0.1–0.3 μm, though the particle size distributions were not well-controlled or well-characterized. , On the contrary, some other studies have indicated that the anatase phase of TiO 2 is more active than rutile, , though it is noted that in both cases catalysts were classified as anatase or rutile on the basis of bulk measurements, while more detailed experiments have indicated that even bulk anatase may contain rutile at the surface . Despite the lack of consensus regarding the active phase, a common observation is that high pretreatment temperatures (∼1000 °C) are required and that small amounts (<1%) of iron impurities enhance conversion (Figure b).…”

“…Titania-based catalysts were the first synthesized nitrogen fixation and have received the most attention of any material for photocatalytic nitrogen fixation. Both Dhar and Schrauzer conducted extensive experiments on lab-synthesized metal oxides in addition to their work on soils and sands. − ,, In Dhar’s later works, he evaluated the photofixation process on titania, zinc oxide, and ferric oxide . Again he supplied carbon sources such as glucose and starch in sterile and nonsterile conditions.…”

On the mechanism of nitrogen photofixation at nanostructured iron titanate films

“…This may be the first example of a non-enzymatic nitrogen fixation in nature. 17 Recently we have found that a nanos-tructured thin film of the composition Fe 2 Ti 2 O 7 , prepared from iron(III) chloride and titanium tetraisopropoxide, in the presence of ethanol or humic acids and traces of oxygen photocatalyzes the fixation of dinitrogen to ammonia and nitrate. 18, 19 Since the reaction occurs also in air and with visible light (k > 455 nm), and since the iron titanate phase may be formed by weathering of ilmenite minerals, 20 it may be a model for a non-enzymatic visible light nitrogen fixation in nature.…”

The first 800 million years: Environmental models for early earth

“…Photoinduced oxidation of dissolved Fe2+ by water has been shown to be a source of hydrogen (Braterman et al, 1983). Photoreduction of water by nitrogen to form ammonia on rutile (TiO,) sand has been demonstrated by Schrauzer et al (1983Schrauzer et al ( ,1985 as a source of ammonia, independent of the presence of hydrogen (this reaction also produces oxygen). Rutile is a common component of beach and desert sand; the ammonia formed in the intertidal and wave zone could thus have been effectively transferred into solution in the ocean, which could provide a substantial reservoir of dissolved ammonia (Bada and Miller, 1968) maintained out of equilibrium with the atmosphere.…”